1. Field of Invention
The present invention relates to an integrated circuit package and method of manufacture. More particularly, the present invention relates to an integrated circuit package having a built-up circuit instead of a conventional substrate and a method of manufacturing the integrated circuit package.
2. Description of Related Art
In step with the rapid progress in electronic technologies, high-tech electronic products having more powerful and personalized functions continue to appear in the market. In general, electronic products are designed towards having a lower dead weight, a smaller and slimmer outline, and being easier to carry. The manufacturing of integrated circuits (IC) is a major stage in fabricating most electronic products. ICs may be packaged into a variety of forms including dual-in-line (DIP) package, ball grid array (BGA) package, and tape automatic bonding (TAB), with each having a particular usage.
In a ball grid array (BGA) package, solder balls are attached to the lower surface of a substrate instead of having a conventional lead frame with leads. Bonding pads on a silicon chip are connected to respective contact points on the substrate of a BGA package either through wire bonding or a flip chip connection. Through trace lines inside the substrate, the contact points on the substrate are re-wired to other contact points on the surface of the substrate. The contact points on side of the substrate are electrically connected to contact points on the other side or the lower surface of the substrate through vias. Finally, solder balls are planted onto the contact points on the lower surface. Because the entire lower surface may be used to distribute contact points in a ball grid array package, a high pin count package is produced. Since surface tension produced by solder balls during a reflow operation has an auto-alignment effect, greater misalignment can be tolerated. In addition, good electrical connection between the solder balls and bonding pads on the chip is one of the reasons for the popularity of BGA packages in IC fabrication.
FIG. 1 is a schematic cross-sectional view of a conventional ball grid array package. A ball grid array package 100 having a chip 200 attached to the backside of a substrate 110 is provided. Bonding pads 202 on the chip 200 connect electrically with corresponding contact points on the substrate 110 by conductive wires 120. The conductive wires 120 are formed in a wire bonding operation. Packaging material 130 encloses the chip 200, the conductive wires 120 and the contact points 112. Solder balls 140 are implanted onto the bonding pads 114 on the substrate 110 so that the chip 200 is electrically connected to an external circuit through the conductive wires 120, trace lines 116 within the substrate 110, and the solder balls 140.
FIG. 2 is a schematic cross-sectional view of an alternative conventional ball grid array package. One major aspect is that a flip-chip connection method instead of a wire bonding method is used inside the ball grid array package 101. Bumps 204 are formed on the bonding pads 202 of a chip 200. The chip is flipped over so that the bumps 204 directly contact the contact points 112 on a substrate 110. The chip 200 connects electrically with an external circuit through the bumps 204, trace lines 116 within the substrate 110, and the solder balls 140.
In general, a ball grid array package that uses conductive wires to connect with the chip has bigger signaling time delay due to higher electrical impedance of conductive wires. Hence, performance of the chip may be affected. On the other hand, a ball grid array package that uses a flip-chip structure must provide extra bumps on the bonding pads of the chip and align the bumps precisely over corresponding contact points on a substrate. Therefore, the number of manufacturing steps is increased and production cost is ultimately raised.
Furthermore, a high pin count chip is typically enclosed inside a ball grid array package. Hence, a substrate having fine pitch contact points must be used to connect the bonding pads on the chip with the contact points on the substrate no matter whether the connection is achieved through conductive wires or flip-chip. The trace width of a conventional printed circuit board (PCB) is about 100 μm while the pitch between contact points is roughly between 800˜1200 μm. Yet, the fine pitch contacts in the substrate of a ball grid array package has a trace width of about 30 μm while the pitch between bonding pads is about 150 μm. Therefore, compared with a conventional printed circuit board, cost of producing the substrate with fine pitch contacts is considerably higher. The fabrication cost is estimated to be about 20% of the cost of forming the entire ball grid array package. The cost of fabricating a substrate suitable for forming a flip-chip package is even higher.